Performance comparison of thin-film composite forward osmosis membranes

Forward osmosis (FO) is an emerging low-energy technology. Much effort was given on developing a new membrane material and engineering membrane structure to improve the performance of FO membranes. The performances of two newly developed polyamide-based thin-film composite (TFC) FO membranes were tested and compared with the commercially available cellulose triacetate (CTA) FO membrane. The intrinsic properties of the two TFC FO membranes determined in RO experiments indicate superior performance of the membranes. When tested in FO experiments, TFC membranes delivered consistent results, confirming their outstanding permeability and selectivity properties. The study shows that future studies on membrane fouling will be necessary to have a better understanding of membrane performance and to further optimize membrane properties. © 2013 Copyright Balaban Desalination Publications

Magnetised titanium dioxide (TiO2) for water purification: preparation, characterisation and application

© 2014 Balaban Desalination Publications. All rights reserved. The study of titanium dioxide (TiO2) as a photocatalyst for water purification has attracted significant attention over the past four decades. However, the separation of photocatalyst from water suspension may be difficult, costly and jeopardise the use of this water treatment technology. Recently, the development and production of magnetised TiO2 have been achieved to offer a solution for the photocatalyst separation problem. This paper discusses the preparation techniques, characterisation and the applications of magnetised TiO2. Many researchers have studied magnetised TiO2 photocatalysts but the lack of articles discussing the water purification processes is still slowing any advance in this field. Here, the progress of the scientific research on preparation techniques to coat magnetic particles by materials such as organic polymers, silica, magnesia, and alumina are reviewed to compare and discuss recent findings. The doping of photoactive TiO2 photocatalyst into the magnetic-coated particles is also emphasised. In addition, the characterisation of magnetised TiO2 in terms of physicochemical properties and operating conditions produced by each technique are critically reviewed. Moreover, examples of applications of TiO2 and magnetised TiO2 photocatalyst in water purification are summarised. In general, the effectiveness of organic removal by magnetised TiO2 is still lower compared to single phase TiO2. The future prospect of this field is deliberated to develop a novel, economic and efficient magnetised TiO2 photocatalyst, which has high organic removal properties

Performance analysis of reverse osmosis, membrane distillation, and pressure-retarded osmosis hybrid processes

© 2015 Elsevier B.V. A performance analysis of a tri-combined process that consists of reverse osmosis (RO), membrane distillation (MD), and pressure-retarded osmosis (PRO) was conducted by using numerical approaches in order to evaluate its feasibility. In the hybrid process, the RO brine is partially used as the MD feed solution, and the concentrated MD brine is then mixed with the rest of the RO brine to be considered as the PRO draw solution. Here, the brine division ratio, incoming flow rate of RO, dimensions of the MD and PRO processes, and the supply cost of the MD heat source were considered as influential parameters. Previously validated process models were employed and the specific energy consumption (SEC) was calculated to examine the performance of the RO-MD-PRO hybrid process. The simulation results confirmed that the RO-MD-PRO hybrid process could outperform stand-alone RO in terms of reducing the SEC and the environmental footprint by dilution of the RO brine in locations where free or low-cost thermal energy can be exploited. Despite the need for further investigations and pilot-tests to determine its commercial practicability, this study provides insights into future directions for water and energy nexus processes for energy efficient desalination

Titania Nanomaterials Produced from Ti-Salt Flocculated Sludge in Water Treatment

Titania is the most widely used metal oxide for the applications of pigments, paper, solar cells and environmental purification. In order to meet the demand of a large amount of titania, our group has developed a novel process which could significantly lower the cost of waste disposal in water treatment, protect the environment and public health and yield economically valuable titania. Titanium tetrachloride (TiCl4) or titanium sulfate (Ti(SO4)2) as an alternative coagulant in water treatment has been explored for the removal of various pollutants from contaminated water or wastewater. Flocculation efficiencies of the Ti-salts were superior to those of Al- and Fe- salts with additional benefits in that a large amount of titania can be produced by calcinating the flocculated floc. The produced titania showed high photocatalytic activity for the removal of volatile organic compounds. The large amount of titania can be applied to pigments, environment and construction materials which require a lot of titania usages. This review paper presents an historical progress from fundamental to application in terms of the detailed production process, characterization, photoactivity of titania produced from Ti-salt flocculated sludge, and its various applications. © 2011 Springer Science+Business Media, LLC

Photodesorption of specific organic compounds from titanium dioxide particles in aqueous media

This study investigates the photodesorption of organic compounds (beef extract, peptone, humic acid, tannic acid, sodium lignin sulphonate, sodium lauryl sulphate, arabic gum powder and arabic acid) from TiO2 (1 g/L in water, pH 7). After a period to reach adsorption equilibrium, photodesorption experiments were conducted in a recirculated reactor at a constant flow rate of 150 mL/min with a UV light intensity of 24 W. Photodesorption was observed only for sodium lauryl sulphate (50%), sodium lignin sulphonate (43.47%), beef extract (20.35%) and tannic acid (10.5%) indicating that photodesorption is specific to some organic compounds but not to all. Using liquid chromatography-organic carbon detection, untreated beef extract and sodium lignin sulphonate were found to contain significant amounts of humic substances (∼1,000 g/mol), which decreased in concentration after dark phase adsorption, while a significant increase in low molecular weight (<350 g/mol) concentrations was observed after photodesorption. UV-treated sodium lauryl sulphate photodesorbed to give both higher molecular weight (HMW) and lower molecular weight (LMW) organics. Thus, the HMW fractions of organic compounds decomposed into smaller compounds after UV irradiation, which subsequently desorbed from TiO2 surface. However, untreated tannic acid contained a larger proportion of LMW acids, which shows a high adsorption affinity to TiO2 during adsorption and poorly desorbs upon irradiation. © 2013 © 2013 Balaban Desalination Publications. All rights reserved

Recent advances in osmotic energy generation via pressure-retarded osmosis (PRO): A review

© 2015 by the authors. Global energy consumption has been highly dependent on fossil fuels which cause severe climate change and, therefore, the exploration of new technologies to produce effective renewable energy plays an important role in the world. Pressure-retarded osmosis (PRO) is one of the promising candidates to reduce the reliance on fossil fuels by harnessing energy from the salinity gradient between seawater and fresh water. In PRO, water is transported though a semi-permeable membrane from a low-concentrated feed solution to a high-concentrated draw solution. The increased volumetric water flow then runs a hydro-turbine to generate power. PRO technology has rapidly improved in recent years; however, the commercial-scale PRO plant is yet to be developed. In this context, recent developments on the PRO process are reviewed in terms of mathematical models, membrane modules, process designs, numerical works, and fouling and cleaning. In addition, the research requirements to accelerate PRO commercialization are discussed. It is expected that this article can help comprehensively understand the PRO process and thereby provide essential information to activate further research and development

Effect of flocculation as a pretreatment to photocatalysis in the removal of organic matter from wastewater

Effects of different flocculants (chloride-based salts and ferric and ferrous salts) and initial organic concentration of wastewater on flocculation-photocatalysis hybrid process were investigated. Titanium dioxide (TiO2) adsorption alone, flocculation alone, flocculation followed by TiO2 adsorption, photocatalysis alone, and flocculation followed by photocatalysis removed 60, 72, 80, 85, and 92% of dissolved organic matter (DOC), respectively. The effect of photo-Fenton reaction in removing organic matter was found to be marginal on the flocculation-photocatalysis hybrid system. The organic removal with the flocculation-photocatalysis hybrid system showed similar results for different flocculants such as chloride-based salts, ferric and ferrous salts and there is no comparative beneficial effect. Flocculation followed by photocatalysis removed up to 92% of organic matter. Different initial concentrations of organic matter were significantly reduced by flocculation to a low level before loading to the photocatalysis process. © 2007 Elsevier B.V. All rights reserved

Stability of Fe-oxide nanoparticles coated with natural organic matter under relevant environmental conditions

© IWA Publishing 2014 Manufactured nanoparticles (MNPs) are increasingly released into the environment and thus research on their fate and behaviour in complex environmental samples is urgently needed. The fate of MNPs in the aquatic environment will mainly depend on the physico-chemical characteristics of the medium. The presence and concentration of natural organic matter (NOM) will play a significant role on the stability of MNPs by either decreasing or exacerbating the aggregation phenomenon. In this study, we firstly investigated the effect of NOM concentration on the aggregation behaviour of manufactured Fe-oxide nanoparticles. Then, the stability of the coated nanoparticles was assessed under relevant environmental conditions. Flow field-flow fractionation, an emerging method which is gaining popularity in the field of nanotechnology, has been employed and results have been compared to another size-measurement technique to provide increased confidence in the outcomes. Results showed enhanced stability when the nanoparticles are coated with NOM, which was due to electrosteric stabilisation. However, the presence of divalent cations, even at low concentration (i.e. less than 1 mM) was found to induce aggregation of NOM-coated nanoparticles via bridging mechanisms between NOM and Ca2+

Synthesis and characterisation of potassium polytitanate for photocatalytic degradation of crystal violet

© 2014 . Potassium titanate nanostructures were synthesised by hydrothermal treatment of TiO2 (P25) in KOH and H2O2. As-produced powders were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption methods. Longitudinally-oriented-wire-like structures with a length up to several micrometres and diameters ranging from 10 to 30nm were obtained. Larger size fibrous nanowires resulting from the hydrothermal treatment showed high affinity in adsorbing crystal violet (CV), which was mainly due to their high surface area. The photocatalytic bleaching of CV solution revealed that the wires are photoactive under ultraviolet light irradiation. Macroporous nanowires are considered as effective adsorbents of CV, capable of photocatalytic degradation, and they can be easily separated from the solution by settling

Preparation of titanium dioxide (TiO<inf>2</inf>) from sludge produced by titanium tetrachloride (TiCl<inf>4</inf>) flocculation of wastewater

Sludge disposal is one of the most costly and environmentally problematic challenges of modern wastewater treatment worldwide. In this study, a new process was developed, which has a significant potential for lower cost of waste disposal, protection of the environment and public health, and yield of economically useful byproducts. Titanium oxide (TiO2), which is the most widely used metal oxide, was produced from the wastewater sludge generated by the flocculation of secondary wastewater with titanium tetrachloride (TiCl4). Detailed analyses were conducted to compare TiCl 4, ferric chloride (FeCl3), and aluminum sulfate (Al 2(SO4)3) flocculation. Removal of organic matter and different molecular sizes by Ti-salt flocculation was similar to that of the most widely used Fe- and Al-salt flocculation. The mean size of Ti-, Fe-, and Al-salt flocs was 47.5, 42.5, and 16.9 μm, respectively. The decantability of the settled flocs by TiCl4 coagulant was similar to that by FeCl3 coagulant and much higher than that of Al 2(SO4)3. The photocatalyst from wastewater (PFW) produced by TiCl4 flocculation was characterized by X-ray diffraction, BET surface area, scanning electron microscopy/energy dispersive X-ray, transmission electron microscopy, photocatalytic activity, and X-ray photoelectron spectroscopy. The resulting PFW was found to be superior to commercial TiO2 (P-25) in terms of photocatalytic activity and surface area. The PFW was also found to be mainly doped with C and P atoms. The atomic percentage of the PFW was TiO1.42C0.44P 0.14. © 2007 American Chemical Society